Cent Disease Index Research Articles

Efficacy of plant growth promoting rhizobacteria in in vitro inhibition of Xanthomonas axonopodis pv. glycines and prevention of bacterial pustules of soybean in the field.

Twelve different plant growth promoting rhizobacteria (PGPRs) belonging to Pseudomonas fluorescens and Bacillus subtilis were tested for their efficacy against bacterial pustules of soybean ( Glycine max ) caused by Xanthomonas axonopodis pv. glycines both in laboratory and field conditions. PGPR-10 ( P. fluorescens ), PGPR-3 ( B. subtilis ), PGPR-4 ( B. subtilis ) and PGPR12 ( P. fluorescens ) showed maximum bacterial growth inhibition in vitro (more than 30mm inhibition zone) and increased seed germination (more than 92%). Highest seed germination (above 95%) occurred with the treatment of PGPR-4 ( B. subtilis ), PGPR10 ( P. fluorescens ), PGPR-1 ( B. subtilis ), PGPR-7 ( P. fluorescens ), PGPR-11 ( P. fluorescens ) and PGPR-5 ( B. subtilis ), while plant vigor increased with PGPR-12 ( P. fluorescens) , PGPR-5 (B. subtilis), PGPR-11 (P. fluorescens) and PGPR-3 ( B. subtilis ). Under field conditions, PGPR-12 ( P. fluorescens ) and PGPR-5 ( B. subtilis ) resulted in decrease of per cent disease index and increase in plant yield compared to other PGPR strains.

Exploitation of Plant Products and Bioagents for Ecofriendly Management of Chilli Fruit Rot Disease

Forty four plant species and eight antagonistic organisms were tested against Colletotrichum capsici and Alternaria alternata, the causal agents of fruit rot disease of chilli. In vitro studies indicated that leaf extracts (10%) of Abrus precatorius (Gundumuthu) and Aegle marmelos (vilvum), demonstrated the highest inhibition of spore germination and mycelial growth of these two pathogens. Among the fungal and bacterial antagonists tested, Trichoderma viride isolate 3 and Pseudomonas fluorescens were very effective in inhib- iting mycelial growth of the pathogens in vitro. In the pot culture experiment, two sprays with leaf extract of A. precatorius (10%), first spray 20 days after fruit set and the second spray 2 days after inoculation with the pathogens, resulted in the lowest disease incidence (23.95%) and intensity (27.60 PDI - Per cent Disease Index) as compared to 71.50% incidence and PDI of 78.20 in the control. Among the antagonistic microorganisms two sprays of talc-based formulation of P. fluorescens (2%) were very effective in reducing the disease intensity (35.70 PDI). However, the leaf extracts and antagonistic organisms only ranked next to the fungicide (carbendazim 0.1%) (18.05 PDI). Field evaluation of the effective plant extracts, antagonistic microorganisms and fungicide revealed that spraying with A. precatorius leaf extract (10%) twice, the first spray at the time of fruit set and the second spray 20 days after fruit set caused the maxi- mum disease reduction (25.53 PDI) followed by a single spray of the same leaf extract (10%) on 20th day after fruit set (28.50 PDI).

Sporophytic and gametophytic recurrent selection for improvement of partial resistance to Alternaria leaf blight in sunflower (Helianthus annuus L.)

Alternaria leaf blight, caused by Alternaria helianthi Hanf., is one of the most important diseases of sunflower causing significant yield losses in several tropical countries. Yet, so far, only partial resistance for the disease has been discovered in the germplasm through conventional sporophytic selection. Therefore, the main objective of the present investigation was to compare sporophytic and gametophytic recurrent selection with the aim to enhance the level of resistance to Alternaria leaf blight. The base population was synthesized by random mating three populations- two interspecific derivatives involving different species of Helianthus and one germplasm accession based on their partial resistance to disease incidence. The base population was subjected to 1-2 cycles of both sporophytic and gametophytic selection. The gametophytic selection was practiced by applying pathogen culture filtrate to the stigma and style one hour before pollination. The selection response was measured by scoring the percent disease index at flowering, 15 days after flowering, and at physiological maturity and by quantifying economic yield gain. A significant reduction in mean per cent disease index values and a gain in seed yield were observed for both the types of selection cycles, but more so for gametophytic selection. The populations improved through gametophytic selection appear to be more promising as the pollen selection allowed the selection of rare favorable allelic combinations that would hardly be detected at the sporophytic level. A combination of gametophytic selection and conventional sporophytic selection should be considered as an effective tool in population improvement programs to achieve higher levels of resistance in relatively short time.

Alternaria Blight of Eucalyptus Hybrid and its Management

The present paper deals with Alternaria blight disease of Eucalyptus hybrid and its management. The symptoms of necrosis of leaves and shoots starting from the tip and progressively downwards giving a blighted appearance to the infected leaves and shoots on seedlings at nursery stage were observed. In order to find out an effective management of disease, seven fungicides, viz. Dithane M-45, Difolatan, Zineb, Bavistin (0.2%). Blue copper-50 (0.3%), Captan (0.2%) and Brestan-60 (0.1%) were sprayed on Eucalyptus hybrid seedlings. The results indicated that all the fungicides significantly reduced the disease incidence as compared to control. However, Brestan 60 treatment was found to be most effective which exhibited disease index per cent as 57.0 as compared to control with 86.6 per cent disease index.

Prediction models: Tool for estimation of rust severity in Teak

Prediction models play an important role in forecasting the disease progression in time. The rust of Teak, which was caused by Olivea tectonae, was predicted by Logistic model. For 1-2 year Teak, the estimated Per cent Disease Index (PDI) varied from 1.88 to 47.75 with coefficient of determination r=0.988 and 2.25 to 84.41 with coefficient of determination r= 0.952 for 3-6 year Teak saplings.

Genetics of powdery mildew ( Erysiphe polygoni D.C.) resistance in Mungbean ( Vigna radiata (L.) Wilczek)

Gene effects were estimated for powdery mildew disease reaction in mungbean to know gene action involved for powdery mildew resistance. Six generations (P 1, P 2, F 1, F 2, B 1 and B 2), of three crosses, PIP 3-85-2×TARM 18, AKM 8802×TARM 18 and PM 9339×TARM 18 were grown for recording disease incidence (DI), per cent disease index (PDI) and area under disease progress curve (AUDPC). Uniformity in the trend was observed for these three parameters. AUDPC values revealed differential rate of disease development on various genotypes of mungbean. Highest rate of disease development was observed on AKM 8802 (973.65) and lowest on TARM 18 (323.82). Both additive and dominance gene actions were found to be important in inheritance of powdery mildew resistance (all the three characters) including non-allelic interactions. Duplicate type of epistasis was detected for disease incidence and complementary for PDI and AUDPC in most of the crosses. The selected plants from early segregating generations may be intermated to accumulate resistance genes and to fix resistance at desired level. Due consideration should be given to quantify disease using AUDPC values.

Association between sporophytic reaction to Alternaria helianthi and gametophytic tolerance to pathogen culture filtrate in sunflower (Helianthus annuus L.)

Seven sunflower genotypes comprising of populations and hybrids showing differential sporophytic reaction to Alternaria leaf and stem blight were studied for their gametophytic reaction to pathogen culture filtrate. The sunflower pollen grains germinate well in the liquid medium and give good pollen tube growth in the absence of the culture filtrate. The addition of increasing concentrations of culture filtrate to medium significantly reduced the pollen germination and tube growth in all the genotypes. The reduction in pollen germination and tube growth in vitro due to culture filtrate was more in highly susceptible genotypes L-101 and Morden than the moderately resistant genotypes Acc. nos. 1229, 180 and ISFH-306. Pretreating the stigma and style with the culture filtrate before pollination reduced the number of pollen grains germinating compared to untreated control suggesting toxin stress can be created on the stigmatic surface before pollination. There was correspondence between pollen germination on stressed stigma (in vitro) and sporophytic reaction of the genotype suggesting pollen grain having resistance would germinate on the stressed stigma and fertilise the ovule achieving selective fertilisation. The correlation analysis indicated that there is a negative relation between sporophytic per cent disease index value and gametophytic parameters such as in vitro and in vivo pollen germination, culture filtrate required to inhibit 50% pollen germination and pollen tube growth. The association between pollen and the sporophytic reaction to the disease indicate the possibility of rapid screening of a large number of genotypes by means of pollen assay as an alternate technique with regard to sporophytic disease index in sunflower. The study also indicate the possibility of pollen selection before fertilisation to achieve rapid improvement in disease resistance.

FUNGICIDAL CONTROL OF THE POWDERY MILDEW DISEASE OF BLACKGRAM

To assess the efficacy of different fungicides against powdery mildew of blackgram, both invitro and field evaluation were taken up. Karathane (0.07 per cent), bavistin (0.1 per cent) and topsin M. (0.1 per cent) were highly inhibitory to the conidial germina- tion of Erysiphe polygoni, Karathane was highly effective in reducing the per cent disease index to the maximum level. Bavistin and topsin M. Were next best in restricting disease development. The grain yield was significantly increased by the application of karathane, when compared to all the other treatments.